Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$49.47	6.839%	$52.8533	$52.85	$52.85	$52.90
Purchase #2	$173.59	9.280%	$189.6992	$189.70	$189.70	$189.70
Purchase #3	$55.75	6.126%	$59.1652	$59.17	$59.15	$59.20
Purchase #4	$216.90	13.824%	$246.8843	$246.88	$246.90	$246.90
Purchase #5	$103.86	5.301%	$109.3656	$109.37	$109.35	$109.40
Purchase #6	$114.74	7.446%	$123.2835	$123.28	$123.30	$123.30
Purchase #7	$54.57	4.149%	$56.8341	$56.83	$56.85	$56.80
7 purchase totals =	$768.88		$838.0852	$838.08	$838.10	$838.20